YELLOWSTONE NATIONAL PARK When European settlers wandered upon this otherworld of gurgling mud pits and angry geysers, they described it as a place where "hell bubbled up."
They didn't guess, as geologists believe now, that three times in the past 2 million or so years, hell blasted the Earth's crust here with a fury that can barely be imagined.
Most recently, some 640,000 years ago, Yellowstone's rage toppled mountainsides, changed the course of rivers and sprayed ash ankle deep over all of what is now the Western United States.
So there's understandable interest in whether it might blow again. And when.
Fresh high-technology studies of the underground cauldron and discovery of a bulge on the floor of Yellowstone Lake show anew the region as geology-in-the-making.
There's evidence that the bulge described by one scientist as an "inflated plain" might be throbbing from the pressure that pushed it up in the first place.
That detection has scientists captivated, not frightened, even as it fills amateur geologists with dread.
Those laymen worry that the pressure cooker of Yellowstone is set to burst.
Even smaller blasts say the size of Mount St. Helens that come about every 20,000 years or so can rearrange Yellowstone's scenery. The most recent of those was 70,000 years ago.
Some urge government engineers to gradually vent steam and magma by drilling, rather than wait for a seemingly imminent, giant and calamitous blast.
"If nothing is done there will be an unimaginable disaster," went discussion at one Internet discussion site. But nobody even seems to be thinking about it."
But the geologists who explore the caldera the collapsed supervolcano that is Yellowstone share neither such alarmist doom nor faith in methods for taming the forces boiling underground.
For starters, drilling here would spoil the natural setting of the world's first national park, created in 1872, said park geologist Hank Heasler.
What's more, he said, it would do no good. The magma chamber miles below the park is mostly like a hardened sponge and is essentially self-sealing.
Discovery of the bulge
Government and university scientists dismiss new-born worries about Yellowstone, about the bulge beneath the lake, and about recent changes at the park's Norris geyser basin. Mostly, they marvel at their out-sized laboratory.
They point out that, literally, the landscape of Yellowstone is always shifting. Last year, typical for the era when such measurements have been made, there were about 2,300 earthquakes in the park.
"Geologists usually look at something that formed millions of years ago and is now dead," said Lisa Morgan, a U.S. Geological Survey geologist. "But in Yellowstone, it's something that's happening right now."
The bulge, discovered with newly employed high-tech gadgetry and techniques led by Morgan last year, might be relatively new. Or, she said, it could have formed millennia ago.
"I don't know whether this thing is active now in terms of inflation or not," Morgan said.
So what set off the panic in the it's-time-to-drill crowd? A few combinations of coincidence and research.
First, state-of-the-art mapping revealed some features of Yellowstone that were previously unknown. Next were more obvious changes to the Norris geyser basin that were taking place. Combined with what scientists see as sensational press coverage, these triggered alarm in some circles.
Beginning in 2002, Morgan led a team that produced the first detailed topographical maps of the bottom of Lake Yellowstone a pristine basin fed by 144 mountain streams and drained by the Yellowstone River.
Morgan deployed robotic submarines. She bounced sonar waves off the lake bed and at frequencies that penetrated deeper into that bottom. She ordered magnetic measurements of the rock. The result was a map whose precision befit the digital age.
"It's like having the cataracts taken off of your eyes," she said.
The scientific view was delightful. Through roughly the middle of the lake ran the edge of the Yellowstone caldera, that sunken supervolcano crater, a tad straighter and more to the east than previously thought.
In a northwestern corner of the lake was a spire field, column after column of towers ranging from just more than 3 feet to a little less than about 30 feet wide and sometimes more than two stories high.
Morgan said they were formed around hydrothermal vents, where sulfur-laced, super-heated water jets into the lake. The sulfur attracts bacteria. The bacteria become filled with silica and build layer upon layer stalagmite-style over the eons.
Perhaps most dramatic was the discovery of the bulge, what Morgan labeled an "inflated plain," to suggest it is evidence of pressure from below the lake nudging at the earth's skin.
Roughly the size of a few city blocks, she said it was pocked with hydrothermal vents that demonstrate it is close to the magma chamber below and possibly under more pressure that other places in the caldera.
Like Harry Potter
While scientists were scanning the lake with sonar equipment in September 2003, one long-time Yellowstone researcher noticed an especially strong sulfur scent rising from bubbles in the water. He'd spent years on the lake but never noticed the smell to be so strong.
But the observation came at a time when it was unusual to be on the lake. Researchers typically leave by summer's end. In the fall, the lake is nearing its lowest levels, when there's less mountain runoff to dilute the sulfur-tainted water from underground hydrothermal venting.
"Maybe it's been that way during that season every year for a long time," Morgan said. "We don't know."
Meantime, there was a shift this year in the baffling water table at the Norris geyser basin about 20 miles away leaving some former bubbling areas dry and creating neon green pools elsewhere that can scald to death wayward bison.
With at least one long-dormant geyser spitting to life near a trail, the park was forced to shut off a large portion of the boardwalk that winds through the steamy plateaus.
"Safety first," said Heasler, the park geologist. "The problem is, we don't know what's causing this."
To children, he compares the enigma of Yellowstone geology to the seven volumes that are expected in the Harry Potter series.
"It's as if we're just into the first paragraph," he said. "There's an awful lot we don't know yet."
He emphasizes that discoveries such as the spires and the bulge are newly noticed, not necessarily new. So Heasler said they couldn't be taken as evidence that there had been any radical developments at Yellowstone in recent years.
The shift at the Norris geysers, he said, is the same sort of change that has made the place remarkable since scientists started paying attention. It would be more unusual if things stopped changing.
Still, Heasler said he received several anxious e-mails a week from people worried about an eruption at Yellowstone that could kill millions.
Bob Smith, a geophysics professor at the University of Utah, has been studying what he calls the living caldera" of Yellowstone for decades. He noted that there have been no unusual seismic activities at the park this year that might precede bigger trouble.
"These things don't go like clockwork," said Smith, author of Windows into the Earth: The Geologic Story of Yellowstone and Grand Teton National Parks. "The hazard . . . is almost too small to calculate."